The period from 1939 to 1945 represented the acme of the old style of war, and with it strategy as the purposeful practice of matching military might with political objectives. In its aftermath a number of challenges to this classical paradigm of war emerged, the first in the closing days of World War II. The dropping of atomic bombs on Hiroshima and Nagasaki, Japan, inaugurated a new era of war, many observers felt. Bernard Brodie, an American military historian and pioneering thinker about nuclear weapons, declared in 1946:

Thus far the chief purpose of our military establishment has been to win wars. From now on its chief purpose must be to avert them. It can have almost no other useful purpose.

If that were indeed the case, a strategic revolution would have occurred.

In some ways, nuclear weapons merely made effective the earlier promise of air power—overwhelming violence delivered at an opponent’s cities, bypassing its military forces. Nuclear weapons were different, however, in their speed, their destructiveness, and the apparent absence of countervailing measures. Furthermore, the expense and high technology of nuclear weapons suddenly created two classes of powers in the world: those who wielded these new tools of war and those who did not.

In the ensuing decades, nuclear facts and nuclear strategy had a peculiarly uneasy coexistence. Many of the realities of nuclear weapons—how many were in each arsenal, the precise means for their delivery, the reliability of the devices themselves and of the planes, missiles, and crews that had to deliver them—were obscure. So too were the plans for their use, although a combination of declassification of early U.S. war plans and the flood of information that came out of the Warsaw Pact countries following the collapse of the Soviet Union in 1991 illuminated some of the darkness.

Nuclear strategic thought, however, was far less murky. Those who developed it stemmed less from the military community (with a few exceptions, such as French Gen. Pierre Gallois) than from the civilian academic world and less from the discipline of history than from economics or political science. An elaborate set of doctrines developed to explain how nuclear strategy worked. One such doctrine was “mutual assured destruction” (MAD), the notion that the purpose of nuclear strategy was to create a stable world in which two opponents would realize that neither could hope to attack the other successfully and that in any war both would suffer effective obliteration.

In all cases, the centre of gravity lay with the problem of deterrence, the prevention of adverse enemy behaviours rather than concrete measures to block, reverse, or punish them. Strategic thought now entered a wilderness of mirrors: What behaviour could be deterred, and what could not? How did one know when deterrence had worked? Was it bad to defend one’s population in any way—with civil defense or active defenses such as antiballistic missiles—because that might weaken mutual deterrence? The problem became more grave as additional countries acquired nuclear weapons: Were Chinese leaders deterred by the same implicit threats that worked on U.S. and Soviet leaders? For that matter, did Indians and Pakistanis view each other in the same way that Americans and Soviets viewed each other?

It is likely (although in the nature of things, unprovable) that the looming presence of nuclear weapons prevented a U.S.-Soviet conflict during the Cold War. On the other hand, the highly probable possession of nuclear weapons by Israel in 1973 did not deter an Egyptian-Syrian conventional assault on that country, nor did Britain’s nuclear arsenal prevent Argentina from invading the Falkland Islands in 1982 (seeFalkland Islands War). For that matter, North Vietnam seems to have disregarded American nuclear weapons during the Vietnam War (1954–75).

Initially, nuclear strategy concerned only a handful of states: the United States, the Soviet Union, China, the United Kingdom, and France. These were countries embedded, initially at least, in Cold War alliances. In 1974 India tested a nuclear device; this was followed by competitive testing of weapons with Pakistan in 1998. Israel was understood to have acquired nuclear weapons during the 1970s if not earlier, and North Korea avowed its acquisition of at least one or two weapons in 2002. In 1991 it became apparent that Iraq had a vigorous and potentially successful nuclear program, and a similar Iranian program had been under way. The spread of nuclear weapons amounted effectively to a second nuclear revolution, which may have operated by a different logic than the first. The stylized (though nonetheless frightening) standoff of the Cold War was replaced by a world in which many of the same elaborate safeguards might no longer exist, by nuclear possession on the part of countries that routinely fought one another (particularly in the Asian subcontinent), and by the development of weapons small enough to be smuggled into a country in a variety of ways. By the beginning of the 21st century then, nuclear issues had revived as a subject of strategic concern, if not serious strategic thought. The proliferation of nuclear technology by a Pakistani scientist, Abdul Qadeer Khan, and the development of nuclear weapons by Kim Jong Il’s North Korea shook optimistic assumptions about the ability of the interstate system to stop marginal actors from acquiring and spreading the wherewithal to make nuclear weapons—including the possibility of terrorist groups acquiring such weapons. The overt entry of India and Pakistan into the nuclear club, the generally acknowledged Israeli nuclear arsenal, and the looming Iranian nuclear threat were no less unsettling.

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